Electromyographic analysis of the serratus anterior and upper trapezius in closed kinetic chain exercises performed on different unstable support surfaces: a systematic review and meta-analysis

Background Multiple investigations have compared the electromyographic (EMG) activity of the scapular muscles between stable and unstable support surfaces during the execution of closed kinetic chain exercises. However, these comparative analyses have grouped different unstable surfaces (wobble board, BOSU, therapeutic ball, and suspension equipment) into a single data pool, without considering the possible differences in neuromuscular demand induced by each unstable support surface. This study aimed to analyze the individual effect of different unstable support surfaces compared to a stable support surface on scapular muscles EMG activity during the execution of closed kinetic chain exercises. Methodology A literature search was conducted of the Pubmed Central, ScienceDirect and SPORTDiscus databases. Studies which investigated scapular muscles EMG during push-ups and compared at least two support surfaces were included. The risk of bias of included articles was assessed using a standardized quality assessment form for descriptive, observational and EMG studies, and the certainty of the evidence was measured with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. A random-effects model was used to calculate effect sizes (ES, Hedge’s g). Results Thirty studies were selected in the systematic review. Of these, twenty-three low-to-high quality studies (498 participants) were included in the meta-analysis. The main analyzes revealed, in decreasing order, greater UT EMG activity during push-ups performed on suspension equipment (ES = 2.92; p = 0.004), therapeutic ball (ES = 1.03; p < 0.001) and wobble board (ES = 0.33; p = 0.003); without effect on the BOSU ball. In addition, no effect was observed for SA on any unstable device. The certainty of the evidence ranged from low to very low due to the inclusion of descriptive studies, as well as high imprecision, inconsistency, and risk of publication bias. Conclusion These findings could be applied in scapular muscles strengthening in healthy individuals. The use of suspension equipment achieves higher UT activation levels. Conversely, the use of any type of unstable devices to increase the activation levels of the SA in shoulder musculoskeletal dysfunctions is not recommended. These conclusions should be interpreted with caution as the available evidence showed a low to very low certainty of evidence, downgraded mostly by inconsistency and imprecision.


Rationale
3 Describe the rationale for the review in the context of existing knowledge.

Line 83-109
Objectives 4 Provide an explicit statement of the objective(s) or question(s) the review addresses.

Eligibility criteria 5
Specify the inclusion and exclusion criteria for the review and how studies were grouped for the syntheses.

Information sources
6 Specify all databases, registers, websites, organisations, reference lists and other sources searched or consulted to identify studies. Specify the date when each source was last searched or consulted.

Line 146-149
Search strategy 7 Present the full search strategies for all databases, registers and websites, including any filters and limits used.

Selection process
8 Specify the methods used to decide whether a study met the inclusion criteria of the review, including how many reviewers screened each record and each report retrieved, whether they worked independently, and if applicable, details of automation tools used in the process.

Data collection process
9 Specify the methods used to collect data from reports, including how many reviewers collected data from each report, whether they worked independently, any processes for obtaining or confirming data from study investigators, and if applicable, details of automation tools used in the process.
Line 159-167 10b List and define all other variables for which data were sought (e.g. participant and intervention characteristics, funding sources). Describe any assumptions made about any missing or unclear information.

Study risk of bias assessment
11 Specify the methods used to assess risk of bias in the included studies, including details of the tool(s) used, how many reviewers assessed each study and whether they worked independently, and if applicable, details of automation tools used in the process.

Effect measures
12 Specify for each outcome the effect measure(s) (e.g. risk ratio, mean difference) used in the synthesis or presentation of results.

Synthesis methods
13a Describe the processes used to decide which studies were eligible for each synthesis (e.g. tabulating the study intervention characteristics and comparing against the planned groups for each synthesis (item 5)).
Line 172-175 and Table 1 13b Describe any methods required to prepare the data for presentation or synthesis, such as handling of missing summary statistics, or data conversions.
Line 164-167 and line 210-213 13c Describe any methods used to tabulate or visually display results of individual studies and syntheses. Table 1 13d Describe any methods used to synthesize results and provide a rationale for the choice(s). If metaanalysis was performed, describe the model(s), method(s) to identify the presence and extent of statistical heterogeneity, and software package(s) used.
Line 215-229 13e Describe any methods used to explore possible causes of heterogeneity among study results (e.g. subgroup analysis, meta-regression).
Line 220-224 13f Describe any sensitivity analyses conducted to assess robustness of the synthesized results.

Reporting bias assessment
14 Describe any methods used to assess risk of bias due to missing results in a synthesis (arising from reporting biases).

Certainty assessment
15 Describe any methods used to assess certainty (or confidence) in the body of evidence for an outcome.

Study selection
16a Describe the results of the search and selection process, from the number of records identified in the search to the number of studies included in the review, ideally using a flow diagram.
Line 232-235 and Figure 1 16b Cite studies that might appear to meet the inclusion criteria, but which were excluded, and explain why they were excluded.

Study characteristics
17 Cite each included study and present its characteristics.
Line 241-251 and Table 1 Risk of bias in studies 18 Present assessments of risk of bias for each included study.
Line 255-283 and Table 2 Results of individual studies 19 For all outcomes, present, for each study: (a) summary statistics for each group (where appropriate) and (b) an effect estimate and its precision (e.g. confidence/credible interval), ideally using structured tables or plots.

Results of syntheses
20a For each synthesis, briefly summarise the characteristics and risk of bias among contributing studies.
Line 255-283 20b Present results of all statistical syntheses conducted. If meta-analysis was done, present for each the summary estimate and its precision (e.g. confidence/credible interval) and measures of statistical heterogeneity. If comparing groups, describe the direction of the effect.
Line 287-367 and Figure 2 and 3 20c Present results of all investigations of possible causes of heterogeneity among study results.
Line 371-384 Table 3 20d Present results of all sensitivity analyses conducted to assess the robustness of the synthesized results.

Line 287-367
Reporting biases 21 Present assessments of risk of bias due to missing results (arising from reporting biases) for each synthesis assessed.
Line 371-384 Table 3 Certainty of evidence 22 Present assessments of certainty (or confidence) in the body of evidence for each outcome assessed.

Registration and protocol
24a Provide registration information for the review, including register name and registration number, or state that the review was not registered.
Line 56 24b Indicate where the review protocol can be accessed, or state that a protocol was not prepared.
Line 56 24c Describe and explain any amendments to information provided at registration or in the protocol.

Not apply
Support 25 Describe sources of financial or non-financial support for the review, and the role of the funders or sponsors in the review.

Competing interests
26 Declare any competing interests of review authors. Declared in PeerJ submit process

Availability of data, code and other materials
27 Report which of the following are publicly available and where they can be found: template data collection forms; data extracted from included studies; data used for all analyses; analytic code; any other materials used in the review.
Data used for all analyses: declared in PeerJ submit process